Another TBI running rich

I'll log for a few minutes tomorrow morning. Stock long block. Already talked to builder to see if they did something different, telling him of my woes. He said its all stock.

Timing is at 0. TPS is at .28v instead of what it should be. No idea why but it seems to run better this way....go figure.

I just went out, started it. It started flubbering right when I started it. Here is the log: https://docs.google.com/spreadsheets/d/1kp_xZu8w0LorG03m83NQmjpjbYErETyX_shdKMVkeD0/edit?usp=sharing

Around row #230 it started to clear itself up

opus said:

I just went out, started it. It started flubbering right when I started it. Here is the log: https://docs.google.com/spreadsheets/d/1kp_xZu8w0LorG03m83NQmjpjbYErETyX_shdKMVkeD0/edit?usp=sharing

Around row #230 it started to clear itself up

Click to expand...

Can you confirm if the engine is surging from idle up to 2500 rpm back and forth like it shows in the logs, or is the the engine rpm sticking to idle speeds more or less?

It is surging but not 2500. I posted this video before, but this is what its doing...although this is an older video, it hasnt changed.

https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/ignition-system-wiring-diagram-1

Your problem appears to be an issues with the tach signal being reported to the ecm. You will want to inspect the wire harnesses and conections. maybe you have a broken wire or connection that as it gets warmer it makes the proper connection, but at different temperatures the connection breaks.

You will want to check the white & pink wire harness as well as the 4 wire harness that connect to the ignition module. you will likely need to trace them out back to the ecm. Someone on here should have the pinouts for the ecm connectors. I assume you replaced the distributor, if not the pickup coil and or trigger assy could be another culprit to the bad tach signal. Also double check the ignition coil connections.

Pay close attention to the wire harness looms also, maybe the wires insulation flaked away or even melted them together in a high heat area.

If all that turns up good the tachometer in the gauge cluster could be malfunctioning and corrupting the tach signal going to the ecm.

Hopefully that helps guide you to a solution.

There is no tach.

I have tried multiple distributors.

With that said, if you hadnt read the whole thread, which I dont blame you. This happens like clock work, only for the time period shown. It doesnt happen any other time. Looking at the logs, like you pointed out, the rpms are erratic. Once they settle, everything is good. So now, why would they be erratic? If you are thinking a chaffed wire, then I would have the issue constantly. If you are thinking temperature, there is no temperature change in the short time this happens. Resistance is another thing, but if that were it, it would be constant.

I replaced the coil. That wouldnt be it...in my mind. Not doubting you, just thinking out loud. I'll check connections.

Thanks!

opus said:

There is no tach.

I have tried multiple distributors.

With that said, if you hadnt read the whole thread, which I dont blame you. This happens like clock work, only for the time period shown. It doesnt happen any other time. Looking at the logs, like you pointed out, the rpms are erratic. Once they settle, everything is good. So now, why would they be erratic? If you are thinking a chaffed wire, then I would have the issue constantly. If you are thinking temperature, there is no temperature change in the short time this happens. Resistance is another thing, but if that were it, it would be constant.

I replaced the coil. That wouldnt be it...in my mind. Not doubting you, just thinking out loud. I'll check connections.

Thanks!

Click to expand...

Given the age of the vehicle I have seen wires breakdown in various ways that can be intermittent despite expected logic. Corrosion, carbon buildup, increased wire resistance or actual breaks in the copper of a wire that still conduct part of the time... yes it is a relatively short period of time but most likely a wire or connection issue. Something is causing that erratic tach signal back to the ecm, which in turn will cause the ecm to momentarily respond to provide fuel/spark for that high 2500 rpm instead of the actual 700 rpm it is at hence the rich surging.

Given you have replaced or swaped all the bolt on items, the wiring would be the one thing left untouched/unconfirmed.

If you can figure out what is causing the signal to distort, I bet your issue will go away.

If your not strong on the electrical side of things with reference to the wiring diagram I linked to above. The pickup coil inside the distributor along with the sprocket are responsible for generating the tach reference signal which is fed to the ignition module and then from the module it is sent to the ecm. So somewhere in there lies your problem.

camaro354 said:

If your not strong on the electrical side of things with reference to the wiring diagram I linked to above. The pickup coil inside the distributor along with the sprocket are responsible for generating the tach reference signal which is fed to the ignition module and then from the module it is sent to the ecm. So somewhere in there lies your problem.

Click to expand...

I'm good with electrical but not GM stuff. Now that you explained that, I'm really good. I'll take a peek inside the dist too. If it was easy enough to run another wire to test, I'd be game for that more that I would be chasing wires. If I get the pinout read, I can probably ohm things out.

opus said:

Further more....

I just reset everything again. There is no way I am going to get the proper idle with the TPS set between .58-.59v, not even close. I cut the TPS voltage in half and got an idle I liked. Took it for a drive and it feels better. I know its not supposed to be set like that but I'm going to try it cold in the morning and see what happens.

Click to expand...

Looking at your latest log, you start with your IAC around 150 steps which is pretty far open, and your TPS voltage at 0.235V which means the throttle blades are very far if not completely closed. Just to rule this out, when you adjusted the TPS voltage, you were physically moving the TPS around to change the voltage, and not using the throttle plate adjusting screw to change the TPS voltage? As long as the TPS voltage is less than 1.0V at key on and more than 4.50V at WOT, your PCM shouldn't really care what the voltage is. It just sets 0%TPS to whatever the voltage is at key on.